Properties of polyimide shells made using vapor phase deposition
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Properties of polyimide shells made using vapor phase deposition E. L. Alfonso,a) S. H. Chen,a) R. Q. Gram, and D. R. Harding Laboratory For Laser Energetics, University of Rochester, Rochester, New York 14623-1299 (Received 28 August 1997; accepted 19 December 1997)
Hollow polyimide shells, to be used in inertial confinement fusion experiments, were fabricated by codepositing monomer precursors onto spherical mandrels. Polyimide shells with 700 to 950 mm diameters and 4 to 13 mm wall thicknesses were produced. The shell wall shrunk 20–30% due to imidization. Burst and buckle pressure tests on these shells yielded estimated mechanical strength properties: , 15 GPa elastic modulus and , 300 MPa tensile strength. The permeability of D2 through polyamic acid at 298 K was 7.4 3 10217 mol ? mym2 ? Pa ? s and increased to 6.4 3 10216 mol ? mym2 ? Pa ? s upon curing the shell to 150 ±C. The permeability of D2 at 298 K through vapor-deposited polyimide flat films was 240 times greater than through polyamic acid.
I. INTRODUCTION
The current target-shell material for direct-drive experiments on the OMEGA laser facility is a lowdensity hydrocarbon polymer fabricated using a lowpressure plasma polymerization process. This material meets the immediate requirements for an inertial confinement fusion (ICF) target shell: low density, smooth surfaces (outer and inner), spherical and concentric, and the capability of being fabricated with dopants at discrete radial positions in the shell wall. Future ICF experiments, especially those conducted at cryogenic temperatures, would benefit if the targets possessed additional properties: higher tensile strength, larger elastic moduli, greater room-temperature permeability, greater radiation resistance, higher thermal conductivity and lower electrical conductivity, and greater opacity at 351 nm. These desirable properties will allow targets to be filled more rapidly with an equimolar ratio of deuterium and tritium (DT), be cooled faster to the DT triple point (19.8 K), survive higher temperature gradients in a cryostat, better resist the damaging effects of b-decay from tritium, and more readily accommodate augmented layering techniques such as RF-coupled joule heating. These properties will also allow decreasingly thin-walled shells to be used to contain the DT fuel; the goal is a 1-mm-diameter target with a 1-mm-thick wall. Polyimide is the only polymeric material with the potential for meeting these additional material requirements. Scientists at Lawrence Livermore National Laboratory were the first to suggest polyimide1 targets for the National Ignition Facility (NIF). If targets could be fabricated with the same strength as commercial a)
Also at Materials Science Program and Department of Chemical Engineering, University of Rochester.
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http://journals.cambridge.org
J. Mater. Res., Vol. 13, No. 10, Oct 1998
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polyimide films, then cryogenic targets could be filled and transported at room temperature and froz
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